When a configuration of Dynamic Host Configuration Protocol (DHCP) of a server is changed, the server will send a force renew message to inform at least one client which is connected with the server to renew the configuration of DHCP. When the at least one client receives a force renew message from a server, the client will send a renew message to request new configuration from the server which sends the force renew message without any authentication of determining whether the force renew message is received from a false server.